For most men, the excitement of the royal wedding lies not in what shade of ruffled white Kate Middleton decides to wear, but what Prince Harry will say in his best man’s speech. If it doesn’t contain at least one injudicious reference to Prince William's chopper (after all, he is a search-and-rescue helicopter pilot), the nation will be sorely disappointed.

Perhaps aware of the potential pitfalls, the younger prince said recently that he would be “selective” about his disclosures, for fear of upsetting his grandmother. However, Prince William’s chosen supporter – as best men at royal weddings are traditionally known – did promise to entertain the party by embarrassing his brother and “making him lose a bit of hair”.

As a best man myself later this year, I am beginning to appreciate the delicate balancing act the job requires: how to be witty without being offensive. And with up to 75 per cent of us suffering from glossophobia – fear of public speaking – it’s no wonder people resort to self-help books and yogic chanting to calm the nerves on the day.

So how do you face up to the challenge? First, the speech itself. When you rise to your feet, under intense pressure to be funny, what do you say?

To help, there are ready-made speeches on the internet which can be subtly tailored for the groom in question. Bestmansspeeches.com asks you to fill out a form with questions such as, “What car does he drive, and has he got points on his licence?”, before providing 10 minutes of “original, witty and very funny” material – and a bill for £34.99.

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While the money presumably wouldn’t be a problem for Prince Harry, I’m not sure the content would go down too well. One of the sample jokes on their website is a story about a groom who was in the army rugby team. The punch line? “He especially liked playing with his privates.” Boom, boom.

A spoof Prince Harry speech doing the rounds on the internet (harryleaks.com) begins with a soundalike suggesting that before he proceeds, “granny” should pop in “the royal earplugs” and Prince William “sit tight and hold on to your hair – you’re going to need to”. As warm-ups go, it’s genteel enough to be adaptable to the needs of most best men. YouTube, meanwhile, is full of examples of what not to do: just google “worst best man’s speeches” and get the shivers as the footage unrolls.

Traditionally, the first thing the best man should explain is how he knows the groom, before thanking the bridesmaids and letting the bride’s side know what sort of man she has married. Cue comic anecdotes and jokey one-liners…

John Bowden, author of several wedding-related books, including The Complete Best Man, says that content isn’t everything – it’s all about the delivery. “You don’t want to be vindictive or insulting,” he says. “You certainly don’t want to denigrate the institution of marriage. The key is to smile as you turn the knife.”

He suggests using a few good-natured wisecracks as a prelude to the toast, which should end on a heartfelt high: “If you can change the tone in the final quarter, ramp up the emotion and leave everyone with goosebumps, you will have really succeeded.”

But the hardest part of the speech is getting to your feet and starting. What if I stand up and suddenly dry up/can’t speak/pass out in the mother-in-law’s lap? How does one still the thumping heart and trembling, clammy palms in the long five minutes beforehand?

Caroline Goyder, an actress and author, runs Loud and Clear, a company that helps non-actors perform with poise in everything from board meetings to television shows. Although her clients include executives, MPs and a monarch (she won’t say which one), some 10 per cent – especially around this time of year – have some connection with a wedding.

Intriguingly, a further three per cent of those are brides who are increasingly rejecting their traditional silent role. “It’s much easier for a bride,” she says. “They just have to stand up and tell everyone how they feel – it’s a golden chalice.”

Goyder tells those clients who are consumed with fear the same thing as directors tell actors: “You only have to have the first line in your head.” The rest – if it has been rehearsed – will follow.

Once on your feet, plant them firmly, make eye contact with a few friendly faces, count to three and breathe. “The golden rule is to slow down,” she says. “And pause before a punch-line. It’s the only way to get a laugh, and nerves make it hard to do.”

Aristotle is also helpful here, and still as relevant today as he was 2,000-plus years ago: establish your ethos – your credibility – and then your pathos. Carefully consider what tone to strike with your anecdotes, and if in doubt run your racier ideas past a member of the older generation beforehand.

For the truly nervous best man, there is another, nuclear option: a session with Nikki Slade, another former actress who works as a “voicework facilitator” with the likes of Deutsche Bank and M&C Saatchi. Her methods to help you “free the inner voice” are unconventional. I spent an extraordinary hour in her South Kensington studio, chanting in Sanskrit, while periodically breaking off to stomp round the room, my eyes mercifully closed, and declaring at the top of my voice: “My name is Iain and I’m warm, confident, inclusive and witty.”

Slade started the session sitting at the front of the studio, playing a raagini – an electronic drone machine used in Indian music – while I sang Om Namah Shivaya

(I looked it up afterwards; it means “I have my own inner building”). We also discussed the seven chakras, the Sanskrit word referring to wheel-like vortices ranging from your navel to a third eye above your head, and pretended that there were imaginary people in the room who found my speech boring and had to be acknowledged to be ignored.

It was ridiculous – and fun. But while it helped me to project my voice – there’s nothing like shouting or chanting without inhibition – I’m not sure it’s for me. Or, indeed, for Prince Harry, an earthy soul not known for his connection with his inner voice.

If Goyder has one bit of advice, it is not to drink more than half a glass before the speech. “Dutch courage is a myth,” she says. “I tell all my clients that, and they look at me with hatred. But at least after it’s all gone well, you can drink as much as you like.”